No description available.

Two aspects of teleost respiration have been emphasised in this investigation. Firstly the gill filaments themselves were observed in order to determine whether or not they played an active role in the ventilation of the gill lamellae. The musculature of the filaments was studied, using visual and electronic methods, and continual muscular activity was noted. Two possible functions of these muscles of the gill filaments have been proposed. Secondly, the brain centres which initiate and maintain the respiratory rhythm were investigated. The neural mechanism was found to be much more complex than had hitherto been suspected in the literature. / Thesis / Doctor of Philosophy (PhD)

Cette étude a pour objectif d'évaluer l'efficacité de l'insufflation continue d'oxygène (ICO) comme stratégie de ventilation des victimes d'arrêts cardiaques tout en évaluant les perceptions et obstacles du changement de pratique. Une revue systématique a été effectuée afin de synthétiser les données de l'effet de l'ICO sur le taux de retour à la circulation spontanée (RCS) et d'autres issues cliniques lors d'arrêts cardiaques. Des 3540 articles repérés, 16 études dont 12 expérimentations animales et 4 études avec populations humaines ont été incluses. Aucune association définitive entre l'ICO et le RCS, le RCS soutenu ou la survie n'a pu être démontrée. De nouvelles études sont nécessaires pour évaluer l'effet de l'ICO sur les fonctions neurologiques et la perception de la qualité de vie des survivants d'arrêts cardiaques. Un sondage a été réalisé auprès de 244 techniciens ambulanciers paramédics de la région de la Capitale-Nationale afin d'évaluer leur perception sur les gains et obstacles à l'implantation de l'ICO comme stratégie de ventilation pour la prise en charge des arrêts cardiaques non traumatiques en milieu extrahospitalier. L'ICO a permis une approche simplifiée et plus sécuritaire pour les intervenants et les patients comparativement à la ventilation manuelle. La flexion du tube supraglottique et l'imprécision de la capnographie ont été identifiés comme obstacles. / This study aims to assess the effect of continuous flow insufflation of oxygen (CFIO) as the ventilation strategy in cardiac arrest care and to assess perceived impacts and barriers to its implementation. A systematic review was performed to synthetize the evidence on the effect of CFIO on return of spontaneous circulation (ROSC) and other clinical outcomes in cardiac arrest. Of the 3450 citations identified, 16 studies including 12 animal-model of cardiac arrest and 4 studies with human populations were included. No definitive association between CFIO and ROSC, sustained ROSC or survival could be demonstrated. Further studies should assess the effect of CFIO on neurological function and perceived quality of life of cardiac arrest survivors. A survey was carried out among 244 paramedics in "La Capitale-Nationale" region to assess their perception on gains and obstacles to the implementation of CFIO as the ventilation strategy for non-traumatic out-of-hospital cardiac arrest. The use of CFIO allows a simplified approach and was perceived as safer for the patient and the paramedic compared to manual ventilation. The bending of the supraglottic airway and the imprecision of capnography were identified as barriers.

Fertilization is a common, cost effective treatment for increasing forest productivity within managed forests of the southeastern United States. However, little is known about how fertilization affects the below-ground processes that drive soil CO2 efflux in loblolly pine (Pinus taeda L.). A thorough understanding of below-ground carbon dynamics is necessary for the estimation of net ecosystem productivity and the carbon storage potential of these managed systems. In April 2004, we began monitoring total soil CO2 efflux (EC), heterotrophic (RH), and root respiration (RR) in response to fertilization with diammonium phosphate (DAP). Respiratory components were measured prior to fertilization, weekly following fertilization, and bi-weekly after respiratory components stabilized using a dynamic closed chamber and an infrared gas analyzer. We found that EC differed significantly (P<0.0001) between fertilized and unfertilized plots, but the direction was dependent on date. In the early period of the study, fertilized plot values were lower than control plots. However, by the latter periods fertilized plot values returned to control levels except for one sampling date in March 2005 when fertilized plot values were greater then control plots. Heterotrophic respiration was consistently and significantly (P=0.0002) lower in fertilized plots. Root respiration was significantly (P=0.0597) increased in fertilized plots when analyzed over the study and showed a 20% increase due to fertilization. We concluded that an increase in RR and possibly root biomass was enough to balance the decrease in RH leading to no difference in EC later in the growing season. We performed a pair of greenhouse studies to observe the effects of fertilization in the form of diammonium phosphate (DAP) on RR. The objectives were to determine how nutrient additions initially affect RR in one-year-old loblolly pine seedlings. Secondly, we wanted to determine if Captan [N-(trichloromethylthio) cyclohex-4-ene-1, 2-dicarboximide], a mild fungicide, could be used to reduce or eliminate ecto-mycorrhizae upon visual inspection. Both studies showed that initially, at a high rate (100 ppm N and 49 ppm P) of fertilization, RR was significantly (P<0.10) increased relative to seedlings that did not receive fertilization. This increase was only temporary with rates returning to, or decreasing below, control levels by the end of the study. No consistent trend was found between low (25 ppm N and 13 ppm P) and moderate (50 ppm N and 25 ppm P) rates of fertilization. Captan was shown to generally have no affect on RR. Captan and fertilization both showed (visual inspection) a decrease in fine-roots and mycorrhizae, which could explain the reduction in respiration rates observed in these treatments by the end of the studies. / Master of Science

Soil carbon dioxide efflux resulting from microbial and root respiration is a major component of the forest carbon cycle. We undertook this investigation to better understand the nature of soil carbon dioxide efflux of plantation loblolly pine, an important ecological and economical resource in the southeastern United States. Specifically, we hoped to learn how soil carbon dioxide efflux differs both spatially and temporally for four age classes of plantation loblolly pine on the Virginia piedmont. During a 12-month period, soil carbon dioxide efflux was repeatedly measured for four age classes of plantation loblolly pine using a dynamic, closed-chamber infrared gas analyzer. The age classes examined were 1- to 2-year-old, 4- to 6-year-old, 8- to 12-year-old, and 20- to 25-year-old stands. Mean soil carbon dioxide efflux rates measured during the 12-month study were 1.72, 2.58, 2.84, and 2.90 micromole/sq m/s for 1- to 2-year-old, 4- to 6-year-old, 8- to 12-year-old, and 20- to 25-year-old stands, respectively. Stand age had a significant effect on efflux rate during 10 of the 12 monthly sampling sessions. Additionally, mean efflux rates were consistently higher near the tree and a significant positional difference was detected during 8 of the 12 monthly sampling sessions. Mean soil carbon dioxide efflux rates, by position, for the 12-month study were 2.72 and 2.28 micromole/sq m/s for the near and away measurement positions, respectively. Based on monthly mean soil carbon dioxide efflux rates, annual carbon losses were estimated at 651, 976, 1074, and 1082 g C/sq m/yr for 1- to 2-year-old, 4- to 6-year-old, 8- to 12-year-old, and 20- to 25-year-old stands, respectively. Regression analysis was used to examine the influence of soil and climatic factors on seasonal changes in soil carbon dioxide efflux. The most influential factors affecting soil carbon dioxide efflux during the 12-month study were soil temperature, soil moisture, stand age, and measurement position. We believe respiring roots significantly influence soil carbon dioxide efflux of plantation loblolly pine and account for differences observed between stands of different ages as well as spatial differences observed within a given stand. / Master of Science

No description available.

Call number: LD2668 .T4 1985 B63 / Master of Science

Call number: LD2668 .T4 1985 M3775 / Master of Science / Electrical and Computer Engineering

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Chapter 1 presents a general literature review on the acute isocapnic hypoxic ventilatory response (HVR). The main findings from Chapter 2 indicate that our modified breathing circuit effectively measured the HVR while maintaining isocapnia. The measured ventilatory variables changed significantly with repeated short-term exposure to hypoxia over a 30-minute period, and the within- and between-day variability did not differ significantly. Furthermore, the variability in the HVR response (as measured by the coefficient of variation, (CV» amounted to approximately 27% between tests in both parameters. Repeated measures are recommended in future determinations of the HVR. In Chapter 3 the main findings were that hypoxic sensitivity does not differ between Caucasian and Xhosa sea-level populations in South Africa, and that ventilatory components in both normoxia and hypoxia differed between these two populations. Two distinct patterns of breathing were evident: shallow, rapid breathing among Xhosa subjects, and deeper, slower breathing among Caucasians. Moreover, lower arterial oxygen saturation levels during hypoxia among Xhosa subjects suggest that these two patterns of breathing differ in the effectiveness with which they oxygenate the blood. Inter-individual variation in HVR within each population is of the same high magnitude as that reported in the literature (Beall et al., 1997), further supporting the use of repeated measures in future studies. As previously reported (Sahn et al., 1977, Reeves et al., 1993), in Chapter 3 I document a significant correlation between HVR and partial pressure of end-tidal CO2 (PETCO). Future studies of HVR should consider PETCO2 as a covariate, despite the fact that my analyses of covariance (ANCOV A) showed no inter-population differences in HVR. In Chapter 4 I report that regression analysis shows that the HVR of parents is not a predictor of that of their offspring. No significant heritability was evident for any of the additional key variables of hypoxic VE ,hypoxic Sa02, and the CV for HVR, but a priori analyses showed that I tested too few subjects to be able to demonstrate heritability (or the lack thereof) conclusively by means of regression analyses. Importantly, repeatability estimates within populations (86 %) revealed that despite its high variability, the HVR is highly repeatable, and therefore remains a useful comparative research tool for studies of human adaptation to hypoxia. / AFRIKAANSE OPSOMMING: Hoofstuk 1 gee 'n algemene literatuuroorsig van die akute isokapniese hipoksiese ventilatoriese reaksie (HVR). Die hoofbevindinge uit Hoofstuk 2 dui aan dat ons gemodifiseerde asemhalingsbaan HVR effektief meet terwyl isokapniese toestande gehantaaf word. Die ventilatoriese veranderlikes gemeet, het betekenisvol verskil met herhaalde korttermyn blootstelling aan hipoksie in a 30-minuut periode, en die binne- en tussen-daagse afwykbaarheid het nie betekenisvol verskil nie. Verder het die afwykbaarheid van die HVR reaksie (soos bepaal deur die koëffisiënt van variasie (KV)) ongeveer 27 % beloop tussen toetse van beide parameters. Herhaalde metings word vir toekomstige bepalings van die HVR voorgestel. In Hoofstuk 3 was die hoofbevindinge dat hipoksiese sensitiwiteit nie verskil tussen Kaukasiese- en Xhosa- seevlak populasies in Suid-Afrika nie, en dat ventilatoriese komponente in beide normoksie en hipoksie verskillend was tussen hierdie twee populasies. Twee definitiewe asemhalingspatrone was duidelik merkbaar: vlak, vinnige asemhaling in Xhosa proefpersone, en dieper, stadiger asemhaling in Kaukasiërs. Verder het laer arteriële suurstof versadigingsvlakke gedurende hipoksie in Xhosa proefpersone daarop gedui dat hierdie twee asemhalingspatrone moontlik verskil in hul effektiwiteit om die bloed met suurstof te verryk. Inter-individuele variasie in HVR binne elke populasie was van dieselfde groot omvang as wat in die literatuur gerapporteer word (Beall et al., 1997), wat die gebruik van herhaalde metings in toekomstige studies verder ondersteun. Soos voorheen gerapporteer (Sahn et al., 1977, Reeves et al., 1993), dokumenteer ek in Hoofstuk 3 'n merkbare korrelasie tussen HVR en parsiële druk van eind-tidale CO2 (PET CO2 ). Verdere HVR studies behoort PET CO2 as a kovariant te beskou, ten spyte van die feit dat my analise van kovariansie (ANCOV A) geen inter-populasie verskille in HVR getoon het nie. In Hoofstuk 4 rapporteer ek dat regressie analise bewys dat die HVR van ouers nie 'n voorspeller van dié van hul kinders is nie. Geen betekenisvolle oorerflikheid was duidelik vir enige van die addisionele sleutelveranderlikes van hipoksiese VE ,hipoksiese Sa02, of die KV van HVR nie, maar 'n vorige analise het getoon dat ek te min proefpersone getoets het om oorerflikheid (of die gebrek daaraan) m.b.v. regressie analises te kan demonstreer. Dit is belangrik dat intra-populasie herhaalbaarheidsskattings (86 %) getoon het dat ten spyte van sy hoë afwykbaarheid, die HVR hoogs herhaalbaar is, en daarom 'n nuttige vergelykende navorsingshulpmiddel is vir studies rakende menslike aanpassing by hipoksie.

Although it has long been recognized that physiological acclimation of photosynthesis and respiration can occur in plants exposed to changing environmental conditions (e.g. light, temperature or stress), the extent of acclimation in different tissues (i.e. pre-existing and new foliage) however, has not received much attention until recently. Furthermore, few studies have investigated the extent of photosynthetic and respiratory acclimation under natural conditions, where air temperatures vary diurnally and seasonally. In this study, the effects of variations in temperature on respiratory CO2 loss and photosynthetic carbon assimilation were examined under both controlled and natural environments. The purpose of the investigations described in this thesis was to identify the effects acclimation would have on two key metabolic processes in plants exposed to temperature change, with emphasis also placed on the role of nutrition (nitrogen) and respiratory enzymatic characteristics on the potential for acclimation in two contrasting tree species, Pinus radiata and Populus deltoides. Controlled-environment studies (Chapter 2 and 3) established that rates of foliar respiration are sensitive to short-term changes in temperature (increasing exponentially with temperature) but in the longer-term (days to weeks), foliar respiration acclimates to temperature change. As a result, rates of dark respiration measured at any given temperature are higher in cold-acclimated and lower in warm-acclimated plants than would be predicted from an instantaneous response. Acclimation in new foliage (formed under the new temperature environment) was found to result in respiratory homeostasis (i.e. constant rates of foliar respiration following long-term changes in temperature, when respiration is measured at the prevailing growth temperature). Available evidence suggests that substantial adjustments in foliar respiration tend to be developmentally dependent. This may in part explain why respiratory homeostasis was only observed in new but not in pre-existing tissues. Step changes in temperature (cold and warm transfers) resulted in significant changes in photosynthetic capacity. However, in stark contrast to the findings of respiration, there was little evidence for photosynthetic acclimation to temperature change. The results obtained from field studies (Chapter 4) show that in the long-term over a full year, dark respiration rates in both tree species were insensitive to temperature but photosynthesis retained its sensitivity, increasing with increasing temperature. Respiration in both species showed a significant downregulation during spring and summer and increases in respiratory capacity were observed in autumn and winter. Thermal acclimation of respiration was associated with a change in the concentration of soluble sugars. Hence, acclimation of dark respiration under a naturally changing environment is characterized by changes in the temperature sensitivity and apparent capacity of the respiratory apparatus. The results from controlled and natural-environment studies were used to drive a leaflevel model (which accounted for dark respiratory acclimation) with the aim of forecasting the overall impact of responses of photosynthesis and respiration in the long term (Chapter 5). Modellers utilise the temperature responses of photosynthesis and respiration to parameterize carbon exchange models but often ignore acclimation and use only instantaneous responses to drive such models. The studies here have shown that this can result in erroneous estimates of carbon exchange as strong respiratory acclimation occurs over longer periods of temperature change. For example, it was found here that the failure to factor for dark respiratory acclimation resulted in the underestimation of carbon losses by foliar respiration during cooler months and an overestimation during warmer months - such discrepancies are likely to have an important impact on determinations of the carbon economy of forests and ecosystems. The overall results substantiate the conclusion that understanding the effect of variations in temperature on rates of carbon loss by plant respiration is a prerequisite for predicting estimates of atmospheric CO2 release in a changing global environment. It has been shown here that within a moderate range of temperatures, rate of carbon uptake by photosynthesis exceeds the rate of carbon loss by plant respiration in response to warming as a result of strong respiratory acclimation to temperature change. This has strong implications for models which fail to account for acclimation of respiration. At present, respiration is assumed to increase with increasing temperatures. This erroneous assumption supports conclusions linking warming to the reinforcement of the greenhouse effect.